Looks like a pricing error on the Xbox Live Costa Rica store.
Injustice is currently free. Great game, for this price I would heartily recommend it!
Here are some instructions on how to go about this kind of region swapping business:
On your computer make a new Windows Live account with Costa Rica as your region (an Outlook address is easiest).
On your Xbox make a new profile, again with Costa Rica as your region.
Use the Outlook address when you have to enter an email.
Go to the tab that lets you press Y to search.
Search for Injustice. The first thing on the list should be the full game. Click download and make sure the file size is 7.8 gigs or thereabouts.
On your computer go to the Xbox account migration page. Sign in with the email address you created in step 1 and change your region to Australia.
Signing in to the account migration page probably booted you out of your Xbox profile, so go back to your Xbox and sign in again. You should see the AUS storefront and the game should still be in your download queue.
NOTE: I posted this deal before actually trying this for myself. Plenty of people have been claiming it works though, but surely it won't last long.
EDIT: Costa Rica store no longer works, but Slovakia does.
EDIT 2: Ikaruga is also there for free!
Got it a few hours ago and can confirm it works.